Tin Mills

Tin Mills

It has been argued that on Dartmoor tin has been extracted since prehistoric times although there is at the moment very little evidence to back this up. The earliest form of tin extraction was by means of working the rivers and streams for alluvial Cassiterite from which the tin was extracted. In the early days of tinning the ore which was being taken from the various water courses was of a high grade and needed little processing before being smelted in small, outdoor furnaces. As this supply gradually ran out it meant that the poorer quality ores had to be used to supply tin for what was fast becoming a very lucrative business. As the available ores were so inferior it meant that they had to be subjected to a higher degree of processing, especially in the crushing stage. In turn this led to a much more mechanised degree of manufacture which involved what at the time was regarded as innovative machinery for crushing and smelting. It therefore became necessary to house this equipment in some sort of building and so the mills came into existence. As always, just to confuse things slightly, there were three main types of buildings where the tinning process took place:

The most common crushing process on Dartmoor was carried out by the use of ‘stamps’ which were literally vertical hammers that were driven by water power in a stamping mill. In the early days of tin production the crushing stage of the operation was most likely to have been done manually with a hammer. As time ticked by and the demand for tin grew there became the need to speed up the process by mechanical means. This was achieved by dropping a vertically set of reciprocating timber balks which were first raised and then released onto the tin ore below, these were the stamps. Each stamp would have an iron ‘cap’ to reduce the wear caused by the continual dropping action. The alternating action of the stamps was produced by the use of a drive shaft with protruding ‘lifters’ which would engage with wooden pegs placed at the back of the timber balks, this in effect lifted each stamp and dropped it. The power used to work the stamps came from water that had been carried by a  leat to a water wheel which in turn was geared up to turn the drive shaft. The stamps usually came in sets of two or three which were arranged in a row and the ore was manually placed under them by the tinner. Georgius Agricola (aka Georg Bauer) depicted these early stamps in his book of 1556 – see HERE, Newman, 1998, pp. 40 – 42. Sometimes stamping mills were referred to as knocking or knacking mills, the word coming from the middle English word Knakke which meant to strike or crack. Several of these have become Dartmoor placenames such as; Knocking Mill Combe and Knackersmill Gulf.

An alternative way of crushing the tin ore was to place it between two large circular granite stones, the upper one of which rotated around the static lower one, this was known as crazing and took place in a crazing mill. The upper stone was slightly smaller and had a hole at its centre with four smaller ones diametrically placed in pairs around the edge. The larger bottom stone simply had a corresponding central hole to that of the upper stone. It is thought that the ore would have been fed through the larger, central hole in the top stone which was then rotated by means of cranks set into the four smaller holes that in turn were attached to the water wheel. The circular motion of the grinding meant that the fine tin ore would collect around the edges of the bottom stone ready for smelting. Although of a slightly different nature, Georgius Agricola also depicts this method in his works of 1556 – see HERE. This means of crushing the ore meant that only the finer and purer alluvial gravels could be processed in this manner. So far there have only been three examples of this kind of mill found on Dartmoor these being at Sheepstor, Outcombe and Gobbet, sadly the Outcombe example has been removed. Newman, 1989, p.44.

A later improvement to the stamping mill came with the use of a ‘stamps box‘, this was simply a wooden box partially sunk into the floor underneath the stamps. At one end of the box was a fine mesh whose purpose was to let pass the fine grains of ore thus separating it from the waste. Initially the ore would be placed in the stamp box and the stamps would begin their pounding, all the time this was happening a flow of water would pass through the box thus washing the crushed ore and waste to the sieve at the end where it was separated.

The whole effect of this innovation was that there would have been no need to stop the stamps in order to remove the crushed ore as was previously the case. It is thought that this new process known as wet stamping was first invented by a German named Sigismund Maltitiz in 1512 again this is depicted in 1556 by Georgius Agricola – see HERE. This speedier and more efficient process of wet stamping probably resulted in the demise of the crazing mills as now even the purer ores could be produced by stamping, Newman, 1998, pp. 42 – 43.

Once the ore had been crushed fine enough the next requirement was that it had to be separated from the valueless sands which were known as gangue, this operation was known as dressing. This was achieved by working on the principle that the particles of cassiterite were heavier than the gangue and when subjected to flowing water will sink faster thus leaving the unwanted materials to be carried away by the moving water. In the days of dry stamping this probably was done with the use of wooden tubs or troughs. However, on the introduction of the wet stamping process the dressing process consisted of the crushed cassiterite passing from the grate of the stamping box via a channel into a long rectangular pit or trough known as a buddle. Here the tin would collect at the head whilst the lighter particles of gangue were washed away with the flowing water. The tin was then taken out of the and the whole process was repeated in further buddles until finally the virtually pure particles of tin were left, Newman, 1998, pp.45 – 49.

Tin Mills

The last type of building was the blowing house which contained the furnace used to smelt the ore, on Dartmoor these were also known as Jew’s Houses. This name came about from the idea that the early Phoenicians came to Dartmoor in search of tin. It has been suggested that blowing houses were a result of technical innovations applied to the smelting process which meant the tin only had to be smelted once to remove the impurities. The old method involved a double smelting process which was both time consuming and costly and was due to the inability to maintain the high temperatures needed in order for the tin to be extracted and the impurities removed. But what was this new innovation? Simply the use of bellows which would allow the furnace to reach and maintain the high temperatures required for the smelting process. The basic design of a blowing house would have been with the water wheel and bellows at the back of the building with a furnace and hearth infront of these and placed inside the room not encompassed in the walls as shown below:

Tin Mills

The smelting operation would have been to firstly pack the furnace with layers of cassiterite (tin ore), peat and charcoal, the latter two elements acted as both a fuel and a flux. The fire was then lit and the water from the leat let out to power the water wheel, this then turned and by a series of cams and counter weights worked the bellows which gave a forced supply of air to the furnace. The furnace needed to reach a temperature of between 1200º and 1300ºC in order to release the tin, a single smelting being known as a tide. Once this had been achieved the molten tin would flow from the furnace and was collected in a flat topped granite trough known as a floatstone, this was located in the bottom of the furnace. From here the tin would then be ladled into rectangular hollows that had been cut into large, flat-topped slabs of granite known as mouldstones. Some of these had a groove cut into the rim of the moulstone’s narrow side, it is thought that a stick would then be placed into the groove and would protrude both inside and outside of the mould. The molten tin was then poured into the mouldstone and the ingots would be cast. If the mouldstone was the type with a groove and stick the resulting ingot would have had a hole running through it which enabled the ingot to easily be removed from the mould and was also a way of tying the ingot to a packhorse. Some of the Dartmoor mouldstones also had additional and smaller moulds on their upper surface it has been suggested that their purpose was to act as sample moulds from which the purity of the tin could be assessed. Alternatively it is just possible they were used to make small ingots of tin which could be easily hidden and then illicitly sold in order to avoid paying the tax on them, (Newman 1998, pp 35 – 40). It has been suggested that the early blowing houses roofs were made of timber and turf and that at the end of the mills’ life it would be set alight and all the fine particles of tin that has accumulated in it was retrieved. This was possible because these fine particles would be carried up into the roof by the heat and smoke of the furnace and then attaching themselves to the wood and turf.

Incidentally, one of the earliest pieces of documentary evidence for a blowing house comes from a lease dating back to 1514 where it states, ‘ibiden vocatum a blowyng myll and knakkyng myll‘, (Newman, 1998, p.7).

The siting of stamping and crazing mills and blowing houses was vital with the first consideration being a constant supply of water to power the various pieces of machinery. Therefore the majority of them were located close to a stream and were built into the base of a natural slope that formed the edge of a river valley. The reason for this was that the slope would provide a steep enough gradient that would allow the water to be leated to the top of the water wheel. In some cases if there was no such natural slope then an artificial one would be created. Logistically it was also useful to have the building close to the source of the tin thus saving time and effort in transporting the ore. The water wheels were housed in narrow stone-lined wheelpits that were normally attached to the exterior wall of the mill although in a few cases the wheel was located in the centre of the building. These water wheels ranged in size from between 8 and 10ft in diameter with a width range of between 1ft 6″ and 2ft. The water to turn the wheels would firstly be leated in from a natural water source and then delivered onto the wheel by means of a wooden channel known as a launder.

Today there are still various forms of field evidence for the early tinning industry to be found on Dartmoor, most of which are the various granite artefacts. At this point it may be as well to describe how William Crossing described blowing houses in the late 1800s:

Small buildings in which tin was smelted on the moor, and worthy of examination as throwing much light on the manner of working adopted by the medieval tinners. They are oblong in form, and the door is invariably near one corner and in one of the longest sides. The remains of a furnace can occasionally be seen, and perhaps a recess in the wall. Some examples have mould stones and pounding troughs in or near them. Sometimes a wheelpit adjoins, and leading towards this a partly choked water course may be traced… The size of these blowing houses varies; some are small, and others as much as 26 or 27 feet long, and about half that in width.‘, 1990, p.12.

As noted above, by far the most common sort of evidence is the structural remains of the tin mills and their associated features. Newman, (1998, p.30) estimates that: ‘structural remains from over 50 tin mills survive on Dartmoor as well as a further 30 sites where artefacts or other evidence indicate the former location of a mill.’ The structural remains are likely to be the lower courses of walls, dried up leat beds, wheelpits, or evidence of waste materials known as tin slimes that had been discarded after being separated in the dressing process. The latter tends to be a fine, silvery or white sand which can sometimes be found downstream of a mill in a layer of an eroded river bank.

A lot of the equipment used in the early tin mills was made of wood such as the launders, stamp balks, waterwheels, races, troughs and tubs so naturally these will have rotted away over time. However, on the other hand some of the equipment was fashioned from moor granite which has not been lost to the ravages of time. Therefore examples of mouldstones, furnace bases, mortar stones, and crazing mill stones to name but a few.

Below is a list of 96 mills that are on Dartmoor and date back to 1750 or earlier, by no means is this a comprehensive gazetteer as many other examples will have been lost, destroyed or are waiting to be discovered.

Location Grid Ref. Date   Location Grid Ref. Date
AVON DAM MILL SX 6722 6553 Pre 1750   MERRIVALE MILL (B) SX 5527 7624 Pre 1750
BAG PARK MILL SX 722     783 Pre 1750   MERRIVALE MILL (C) SX 5518 7665 Pre 1750
BLACK LANE BROOK MILL SX 6290 6690 Pre 1750   METHERAL MILL SX 6682 8402 Pre 1750
BLACK TOR FALLS MILL (L BANK) SX 5749 7161 Pre 1750   METHERAL MILL (B) SX 6697 8412 Pre 1750
BLACK TOR FALLS MILL (R. BANK) SX 5748 7162 Pre 1750   MICHELCOMBE MILL SX 6995 6880 Pre 1750
BLACKA BROOK MILL SX 564     644 Pre 1750   NEWLEYCOMBE MILL SX 5893 6986 Pre 1750
BLACKALLER MILL SX 7377 8377 Pre 1750   NEWLEYCOMBE MILL (B) SX 5713 6952 Pre 1750
BLACKATON BALL MOOR MILL SX 6884 7812 Pre 1750   NORSWORTHY BRIDGE MILL SX 5673 6938 Pre 1750
BRADFORD MILL SX 700     910 Pre 1750   NORSWORTHY BRIDGE MILL (B) SX 5687 6942 Pre 1750
BRIMLEY MILL SX 8010 7712 Pre 1750   NORSWORTHY MILL SX 5678 6958 Pre 1750
BRISWORTHY MILL SX 5602 6469 Pre 1750   NORSWORTHY MILL (B) SX 5674 6954 Pre 1750
BROAD FALLS MILL SX 6545 6692 Pre 1750   NUNS CROSS FORD MILL SX 6105 6988 Pre 1750
BURRATOR LODGE MILL SX 5519 6852 Pre 1750   OUTCOMBE MILL SX 5801 6860 Pre 1750
BUTTERBROOK MILL SX 6422 5920 Pre 1750   OUTER DOWN MILL SX 6821 8658 Pre 1750
CASELY MILL SX 7887 8216 Pre 1750   PARKTOWN MILL SX 547     732 Pre 1750
CHAGFORD BRIDGE MILL SX 6950 8778 Pre 1750   PITTON MILL SX 7210 7852 Pre 1750
CHALLACOMBE MILL SX 6933 7941 Pre 1750   PIZWELL MILL SX 6686 7849 Pre 1750
CHALLACOMBE MILL (B) SX 6940 7961 Pre 1750   PLASTER DOWN MILL SX 5168 7225 Pre 1750
COLESMILL MILL SX 5937 6676 Pre 1750   PLYM CONSOLS MILL SX 5858 6990 Pre 1750
COLLEYTOWN MILL SX 5668 6748 Pre 1750   PLYM STEPS MILL SX 6030 6725 Pre 1750
COLLY BROOK MILL SX 5423 7782 Pre 1750   RED BROOK MILL SX 6694 6279 Pre 1750
COMBESHEAD MILL SX 5850 6838 Pre 1750   RIDDIPIT MILL SX 5702 7016 Pre 1750
DEAN MOOR MILL SX 678     653 Pre 1750   RIDDON MILL SX 6741 7668 Pre 1750
DOE TOR GREEN MILL SX 5333 8524 Pre 1750   RUDDYCLEAVE MILL SX 7308 7407 Pre 1750
DRY LAKE MILL SX 6400 6337 Pre 1750   RUSHFORD WOOD MILL SX 7024 9002 Pre 1750
DRY LAKE MILL (B) SX 6336 6636 Pre 1750   SOUTH HILL MILL SX 6801 8710 Pre 1750
DUCKS POOL STREAM MILL SX 6293 6766 Pre 1750   SOUTH HILL MILL (B) SX 6783 8685 Pre 1750
EGGWORTHY MILL SX 5435 7183 Pre 1750   SWINCOMBE RIVER MILL SX 6239 7113 Pre 1750
ELFORDLEIGH MILL SX 545     586 Pre 1750   TAW RIVER MILL SX 6205 9197 Pre 1750
FERNHILL MILL SX 5565 6018 Pre 1750   TEIGNHEAD FARM MILL SX 6377 8426 Pre 1750
FISHLAKE FOOT MILL SX 6490 6834 Pre 1750   THORNWORTHY MILL SX 6723 8443 Pre 1750
GLAZEMEET MILL SX 6683 6031 Pre 1750   VENFORD BROOK MILL SX 685     712 Pre 1750
GOBBET MILL SX 6453 7280 Pre 1750   WALLABROOK MILL SX 6716 7957 Pre 1750
GOLDEN DAGGER MILL SX 683     803 Pre 1750   WEEK FORD MILL SX 6619 7234 Pre 1750
GRATNAR MILL SX 7201 8362 Pre 1750   WEEK FORD MILL (B) SX 6618 7232 Pre 1750
GREAT WEEK MILL SX 7145 8760 Pre 1750   WEST CLEAVE MILL SX 6077 9397 Pre 1750
HOOK LAKE MILL SX 6393 6509 Pre 1750   WHEAL CHANCE MILL SX 5955 7000 Pre 1750
IVY TOR WATER MILL SX 6285 9175 Pre 1750   WHEAL DOROTHY SX 6552 6650 Pre 1750
LANGCOMBE MILL SX 6037 6723 Pre 1750   WHITENKNOWLES MILL SX 5859 6696 Pre 1750
LEFT LAKE MILL SX 6413 6273 Pre 1750   WIDECOMBE MILL (B) SX 7194 7683 Pre 1750
LETHER TOR FARM MILL SX 5668 6981 Pre 1750   WIDECOMBE NORTH HALL MILL SX 7184 7690 Pre 1750
LITTLE HORRABRIDGE MILL SX 5149 6962 Pre 1750   WILL MILL SX 5330 8145 Pre 1750
LONGSTONE MILL SX 5600 6876 Pre 1750   YEALM STEPS MILL SX 6179 6352 Pre 1750
LONGSTONE MILL (B) SX 5607 6880 Pre 1750   YEALM STEPS MILL (B) SX 6172 6385 Pre 1750
LOWER HART TOR MILL SX 6048 6743 Pre 1750   YELLOWMEAD MILL SX 5742 6755 Pre 1750
MANGA MILL SX 6409 8478 Pre 1750   YEO FARM MILL SX 5512 6696  Pre 1750
MANGA MILL (B) SX 6399 8467 Pre 1750   YEO FARM MILL (B) SX 5509 6697 Pre 1750
MERRIVALE MILL SX 5527 7535 Pre 1750   YES TOR BOTTOM MILL SX 5669 7295 Pre 1750

It is impossible to cover the subject of early Dartmoor tin mills on a single web page but for anyone interested in researching the topic further there are numerous sources on the topic. The bibliography below lists many of the books and articles written on the early mills but in addition there is the Dartmoor Tinworking Research Group who: ‘promotes research into all aspects of the Dartmoor tin industry and Dartmoor tinners.’ Their website carries details of membership, projects and activities, a link for which can be found opposite. Another useful source of information is the Archaeological Data Service website which lists some of the Dartmoor tin mills with their locations, information sources etc, again this can be found by following the link opposite. Simply enter either stamping mill, crazing mill or blowing house into the ‘what’ box and ‘Devon into the ‘where’ box then click the ‘choose resources’ link, select all, return to search and click ‘click here to search’. You will then be presented with results of either 47 blowing houses, 41 stamping mills or 1 crazing mill.

If you like reading Dartmoor fiction and are interested in the medieval tin industry then a book called, ‘A Moorland Hanging’ by Michael Jecks is just for you. It is a medieval murder mystery set in the tin mines of Dartmoor and gives some excellent portrayals of the subject.

Reference

Crossing, W. 1990. Crossing’s Guide to Dartmoor, Newton Abbot: Peninsula Press.

Hemery, E. 1983. High Dartmoor, London: Hale Publishing.

Newman, P. 1998. The Dartmoor Tin Industry, Newton Abbot: The Chercombe Press.

Bibliography.

Atkinson, B. 1988. Mining Sites in Cornwall and South West Devon, Redruth: Dyllansow Truran.

Atkinson, M., Burt, R., & Waite, P. 1978. Dartmoor Mines, Exeter: Exeter Industrial Archaeology Group.

Bird, R & Hirst P. 1996. The Brimpts Tin Mines, Exeter: The Dartmoor Tinworking Research Group.

Brooke, J. 1980. Stannary Tales, Truro: Twelveheads Press.

Clark, S. 1995. Mining and Quarrying in the Teign Valley, Newton Abbot: Orchard Publishing.

Greeves, T. 1986. Tin Mines and Miners of Dartmoor, Exeter: Devon Books.

Hambling, P. 1995. The Dartmoor Stannaries, Newton Abbot: Orchard Publishing.

Hamilton Jenkin, A. K. 2005. Mines of Devon, Ashbourne: Landmark Publishing.

Hamilton Jenkin, A. K. 1974. Mines of Devon – The Southern Area, Newton Abbot: David & Charles.

Harris, H. 1996. The Industrial Archaeology of Dartmoor, Newton Abbot: Peninsula Press.

Richardson, P. H. G. 1992. Mines of Dartmoor and the Tamar Valley, Sheffield: Northern Mine Research Society.

Walmesley, M. & J. 1982. The Old Men of the Moor, Ilfracombe: Arthur H. Stockwell Ltd.

 

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